Development of a mobile system to provide drinking water in desert areas by the use of hygroscopic salts

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Objective

As the sun rises over the desert certain patches of soil become wet. As the temperature rises further these patches dry up again, but the next morning the process is repeated. This phenomenon is due to the presence of hygroscopic salts at or near the surface which hydrate during the cooler and more humid night. As the temperature starts to rise, these salts dissociate and are dissolved in their own water of hydration. This brine is evaporated in the course of the day, leaving behind anhydrous salts which pick up water again from the moist cool night air. This project will attempt to use such salt systems for the recovery of drinking water in deserts. Cloth or other suitable support material will be impregnated with hygroscopic salts and exposed to the night air. The next morning they will be packed in airtight black boxes and exposed to the sun. The box will be connected to a cooling vessel and the water vapour will condense as clean water.

The project will investigate the type of salt (CaCl2 has already proved to be suitable) and the support systems. Earlier experiments have shown that more than 3/4 litre of water can be obtained each night from 1 m of salt-impregnated cloth. The main part of the study will be concerned with the cooling system for the condenser vessel. Cooling will be carried out either by absorption systems or by vapour compression systems. Absorption systems can be heated directly with abundantly available solar energy, whereas vapour compression systems require conversion of solar energy into electrical energy.

The study will result in the design of a mobile system for the recovery of drinking water in deserts.